Protective dunnage devices for preventing the unwanted shifting of cargo in trucks, railcars and other cargo carriers are typically required when in use to fill relatively large void areas and to reliably block movement of cargo elements such as stacked and palletized loads which fail to fill and conform to the assigned space in the carrier. Expansible cellular or "honeycomb" void fillers made of strong corrugated paperboard stock have met with great favor in the trade because of their light weight and consequent minimum subtraction from cargo weight limits, their low cost, and their collapsibility, which permits compact and economical storage and shipment of the void fillers themselves.
Such honeycomb void fillers are commonly suspended from above when in use, at which time they are generally held expanded by their own weight. See, for example, Hees U.S. Pat. No. 3,618,535, and Farley U.S. Pat. No. 3,823,675. It is a characteristic of such honeycomb void fillers than when expanded in the normal manner the cells in the mid region of the cellular structure tend to elongate vertically to a greater degree than cells nearer the top and bottom, thereby drawing inwardly the sides of the structure and distorting the filler unit to a narrow waisted or "hourglass" outline. This condition can result in failure of the filler to block the dislodgment of cargo items such, for example, as some of the boxes in a stacked load.
Much effort has been directed to overcoming this problem in the most efficient and economical manner, and with means of minimum weight. See, for example, Bramlett U.S. Pat. No. 3,593,671 and Sewell U.S. Pat. No. 4,007,309. Both of the solutions disclosed in the two patents just mentioned require insertion of special elements in the cell structure to resist the hourglassing tendency. Such special elements add to the cost of the structure and do not contribute proportionately to its effective strength.
The present invention has as its principal object the provision of an improved void filler of the cellular type referred to, incorporating means which effectively reduces hourglass-type distortion, but which requires no special inserted or differentiated structural elements, and wherein the resistance to hourglassing is achieved merely by selectively varying the spacing between certain of the glued areas at which the laminae or strips are secured together, the spacing between the glued securance positions being such as to produce a variation of cell wall dimensions which inherently limits the extension and hourglass distortion of the unit.
Other objects and advantages of the invention will become apparent upon consideration of the present disclosure in its entirety.